Inertial Sensor Asymmetric Support for Cavity Distortion
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Solution Overview
Problem
Inertial sensors employing the transfer mold process face issues with asymmetrical distortion and distortion due to high pressure, leading to decreased sensor sensitivity and reliability, as the deformation of the MEMS element affects the detection electrodes and capacitance measurements.
Innovation Solution
The design includes a movable part with symmetrically positioned detection electrodes and a cavity structure that maintains symmetry with respect to the rotation axis, allowing for differential detection of inertial forces while minimizing the impact of environmental deformations, using a three-layer silicon wafer structure with supports to stabilize the movable part and reduce distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the transfer mold process is applied to encapsulate the movable part, then mass productivity and manufacturing cost are improved, but the cavity is deformed due to high pressure and thermal expansion differences
Solution Approach 1:
The movable part is designed with asymmetric support structures positioned at specific locations to counterbalance the symmetric deformation caused by high-pressure resin filling. This asymmetric configuration creates compensating forces that maintain cavity shape integrity during the transfer mold process while preserving mass productivity benefits.
Solution Approach 2:
The patent modifies the geometric parameters of the movable part and cavity structure to accommodate thermal expansion differences between the silicon MEMS element and resin package. By adjusting dimensions and adding compensation features, the system maintains manufacturing precision despite the inherent thermal mismatch in high-volume production.
2Measurement precision
If the movable part is configured asymmetrically to shift the center of gravity, then out-of-plane acceleration detection is enabled, but the structure becomes vulnerable to asymmetrical distortion
Solution Approach 1:
The patent introduces counterbalancing support structures positioned strategically to offset the asymmetric configuration of the movable part. These supports act as counterweights that maintain the center of gravity shift necessary for acceleration detection while preventing asymmetrical distortion that would compromise sensor reliability.
Solution Approach 2:
The movable part incorporates localized reinforcement features at specific positions to resist distortion in critical areas. By applying different structural properties to different regions, the design maintains the asymmetric center of gravity for detection capability while enhancing reliability where distortion is most likely to occur.
3Device complexity
If the detection electrode is positioned under the movable part, then the structure is simplified, but the electrode is subjected to asymmetric distortion reducing detection accuracy
Solution Approach 1:
The patent introduces an intermediary support structure between the movable part and the detection electrode. This intermediary element acts as a mediator that isolates the detection electrode from asymmetric distortion forces while maintaining the simplified under-plate configuration. The support structure transfers only vertical forces while blocking lateral distortion from reaching the electrode.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances the sensitivity and reliability of inertial sensors by reducing asymmetrical distortion and pressure-induced deformation, ensuring consistent capacitance measurements and improved detection accuracy.
Implementation Method 1
a movable part configured to rotate about a rotation axis, which passes through the support, when an inertial force in a detecting direction is applied to the inertial sensor
Implementation Method 2
a capacitance type inertial sensor detects the displacement as a change in the capacitance between a fixed detection electrode and a movable electrode
Data Source
AI summary
A movable part rotates about a rotation axis, which passes through a support, when an inertial force in a detecting direction is applied to an inertial sensor. The movable part includes a first region and a second region displaced in a direction opposite to a direction of the first region when the inertial force is applied. A second substrate includes first and second detection electrodes opposed to the first and second regions, respectively. The first detection electrode and the second detection electrode are provided symmetrically with respect to the rotation axis. A cavity is provided symmetrically with respect to the rotation axis. In a direction perpendicular to the detecting direction and a direction in which the rotation axis extends, a length from the rotation axis to an end of the first region and a length from the rotation axis to an end of the second region are different.